What do you tell men with low but detectable PSA who have completed ADT and RT?

Several analysis have shown that patients who do not achieve undetectable PSA levels after 6 months of ADT have worse outcomes. This is a bit of a moving target and the definition of undetectable has changed over the decades.
An important question is - are these patients failing due to incomplete local control or do these patients harbor metastatic disease at presentation? I would argue that with modern doses of radiation we may have reached the goal of prostate radiation - to sterilize the prostate of cancer. The ASCEND-RT trial showed that maximizing dose with an LDR brachy boost, outcomes are improved. But this may be the limit of local therapy. I doubt we can squeeze out any much more with biological equivalent doses that were achieved ...